Systems which simulate vehicles are known. Such simulator systems typically incorporate a motion base for providing movement in a limited space, and a driver module mounted on the motion base where a user, or "driver", of the simulator system sits. The driver module may include a mock-up of a vehicle. Movement of the motion base is coordinated with displayed images, thereby providing the driver with a sense that the simulator system is traveling.
Known motion bases are powered by electric or hydraulic actuators. Although electric actuators are capable of generating high forces, and thus strong movements of the driver module, such actuators are expensive and difficult to repair. Thus, faulty electric actuators are usually replaced, adding to the already significant expense associated with the use of such actuators. Hydraulic actuators are difficult to operate and maintain because they require hydraulic fluid which can leak out of the actuators. Furthermore, in conventional hydraulic motion bases for vehicle simulators, it is difficult to achieve "smooth", realistic motion effects in vehicle simulation rides. A motion base incorporating hydraulic actuators is particularly likely to lurch or jerk the driver when simulating a sudden start or stop. Such drawbacks are the result of the fact that hydraulic fluid is incompressible, causing most of the acceleration forces to be ultimately transmitted to the driver. Leakage of the fluid also increases the costs associated with using hydraulic actuators, since precautions against leakage must be taken when transporting the motion base.
Although pneumatic actuators do not suffer the above-described drawbacks of hydraulic actuators, pneumatic actuators have not been used often in motion bases. Since air is compressible, it is difficult to precisely control pneumatic actuators under varying loads and desired motion objectives, such as a desired velocity.
In addition to motion bases, vehicle simulator systems also include one or more user input devices, such as a steering wheel, to control the simulation. For added realism, the steering wheel of the simulator should also generate "feedback" to the driver. This feedback is torque which provides the driver with the same resistance as the forces that would be transmitted from the wheels of an actual moving car through a steering system to the steering wheel. Unfortunately, steering wheel input devices are constrained by many of the same drawbacks as motion bases, as described above. Furthermore, a hydraulic or electric steering wheel input device cannot easily apply a smoothly-varying force, as would the steering wheel of a car.
Another component of vehicle simulator systems is a display system for presenting images to the rider. Such images may represent the vehicle's surroundings, "heads-up" control panel displays, maps and charts, and any other images which enhance the simulator experience. In a car simulator, an image presentation apparatus preferably presents an image in front of the driver in an area corresponding to the windshield of an actual car. One implementation of such a presentation apparatus is to provide a computer monitor or television screen at a location corresponding to the windshield of the car.
It is preferred that the image presentation apparatus present the images in an area corresponding to the windshield because viewing an image at a close range causes the driver to be "immersed" in the image. The image fills the driver's field of view so that the driver is not distracted by other sights. The sense of immersion in the image thus creates a "virtual reality" which is very convincing. Unfortunately, in systems having such monitors directly in front of the driver, the driver sees the displayed images at a very close viewing distance in the "near field", causing eye strain. Such eye strain problems are common when, for example, viewing large front-screen or rear-screen projections at a close range.
A video screen at a close viewing distance is further disadvantaged by an inability to present images having "depth". Without a large distance between the presented image and the viewer, the presented images are not in the "far field" and thus have no depth. Without a perceived "depth" in the image, the driver cannot approximate distances within the image, resulting in an unrealistic simulation. In addition, small video screens or computer monitors cannot provide a large enough image to immerse the driver, while large video screens are prohibitively expensive.
Still another component of vehicle simulator systems is an image generator. The above-described presentation apparatus for presenting images cooperates with the image generator which creates the images. In known car simulator systems, the generated images are merely computer-generated graphics which do not resemble video or photographic quality images. Known car simulator systems are thus not very realistic because of the low quality of images generated by such systems. Computers capable of generating realistic, video quality images in real-time are very expensive, and thus not feasible for use in an entertainment device such as a race car simulator. Less expensive computers either cannot generate realistic images, or generate images at a rate which is too slow to provide the appearance of continuous motion.
Other image generators generate images in accordance with pre-recorded video or film images. Although these images are realistic, the images are predetermined and cannot be manipulated. For example, such image generators cannot show an image from a different point of view than that of the original recording. Thus, these image generators are unacceptable for use with interactive car simulator systems since they are unable to display images which change in accordance with the driver's action.
The image generator in an interactive car simulator system must display images of scenery, such as a race track and surrounding landscape, as well as images of visual elements, such as other cars, which move independently against the background of the scenery. Image generators in known interactive simulators are unable to display realistic, independently-moving visual elements. As described above, known image generators either use computer-generated graphics for the visual elements, or use static, pre-recorded photographic images of visual elements.
While computer-generated graphics are unrealistic, too expensive or too slow, pre-recorded photographic images are limited in that they cannot show visual elements from arbitrary points of view, as is required in an interactive simulator system. Though such pre-recorded images may be moved within the "virtual world" of the scenery, they cannot exhibit perspective shifts which would occur as the visual elements move. One attempt to ameliorate these drawbacks of pre-recorded images is to use pre-recorded video `clips` which are a series of images of a visual element at different sizes. However, even if the image generator uses pre-recorded video `clips` of visual elements, such clips are also static and do not allow for dynamic, interactive changes in perspective.